Production of hydrocyanic acid



patented Oct. 1 7, 1933;

UNITED STATES 1 f 1,931,441 1 PRODUCTION OF HYDItocYA'mo non) Konrad Keller, Dortmund-living, Germany, as signor 'to Gesellsc'haft Fur Kohlentechnik m. b. H., Dortmund-Eving, Germany No Drawing. Application June 6, 1930, Serial N6. 459,611, and in Germany June 6, 1929 5 Claims. (cur-151);

The object of the present invention is a process for the production of hydrocyanic acid from ammonium thiocyanate.

It is known that thiocyanic salts are converted 5 into hydrocyanic acid by oxidation or reduction.

The yields obtained by the known processes especially of oxidation with the aid of various .oxidizers are, however, poor. Raschen developed a method of oxidizing potassium, sodium and calcium salts of thiocyanic acid into hydrocyanic acid by means of nitric acid, and obtained generally yields of from 50 to 60 per cent of the theoretical and of over 90 per cent if potassium or calcium thiocyanate was used andcertain special conditions observed. Therefore, the prerequisite for the known process is the manufacture of the corresponding potassium, sodium and calcium salts from NH4CNS. Investigations made of the possibility of converting NH4CNS (ammonium thiocyanate) directly into hydrocyanic acid showed that, unless special measures are taken, reaction with NH4CNS gives but poor results, yields being not more thanfrom 50 to 60 per cent of the theoretical. It was found that only after modifying the known methods, are good results obtainable with the ammonium salt, yields of 90 per cent andupwards being now obtainable according to the present invention.

It was found that, in order to attain this end, it was necessary to maintain certain acid concentrations in the reaction liquid with the utmost accuracy, comparative tests: 0

First test A solution of 16.0 grms. KCNS in 100 c. 0. water and the. theoretical amount of nitric acid (of 1.125 specific gravity) required for oxidation, both of them kept in separate burettes, were dropped into a generating flask in small, adjustable, prorata quantities and in such a way as always to feed the nitric acid somewhat in advance of the KSNS solution. The flask initially contained a solution of 200 c. c. KHSO4 of a strength such as is obtained by interaction of solutions of the above concentration. While introducing the potassium thiocyanate solution and the nitric acid, the flask contents were vigorously stirred and at the same time heated to 'a temperature of as will be seen from the following x 9,0. 0,. and, towards the endof the reactiomto Two such tests made under the same conditions gave yields-of 93.3 and 93.5 per cent respectively.

The reactionliquid wasquite clear anddid not contain any unaltered ammonium thiocyanate afterthe reaction had come to an end.

Second test -A solution of 12.5 grmsNHiCNS in 100 c.-c. waterwas caused tov react with the theoretical amount of :nitricacid (of 1.125 sp. gr.) required for oxidation in exactly the same manner and l at the same temperature as in the first test, with the exception that the said solutions were dropped concentration of at least 1 per cent of. free nitric acid inthe reaction mixture (the so-called bath liquid) where the reaction of the ammonium thiocyanate solution and the nitric acid takes place. This iswell illustrated, for i'nstance, from the following tests for the determination ofthe minimumhnitric acid concentration required for the oxidation of ammonium thiocyanate. An accurately measured quantityvof ,bath'liquid (strength= mol. of. ammonium bisulphate to 100 c. 0. water) was poured in a distilling flask of 100 c. 0. capacity, which, up to thedistilling tube (side tube), was immersed in a beaker -filled with boiling Water. To this flask were added, drop by drop, from two burettes, accurately measured quantities of nitric acid and of ammonium thiocyanate solution (strength: mol. to c. c.) The neck of the flask was stoppered, and a test tube moistened with caustic soda solution was passed over the distilling tube. The gasevolution in the bath liquid of the flask, as well as the appearance of brown nitric oxide gases and finally the detection of cyanogen in the caustic 100 soda solution of the 'receiverindicated in each case the nitric acid concentration at which oxidation of the ammonium thiocyanate occurred.

The following table shows representative results obtained.

Bath liquid= mol. (19.16 gr.) NH4HSO4 to 100 c. c.

NH4CNS solutio=n=% mol. (12.66 gr.) NHiCNS to 100 c. c.

I Nitric acid=23.75 gr. HNOs in 100 c. 0.

Bath liquid HNO; NH4CNS gffif Reaction 0.0. 0.0. 0.0. solution 10 0. 4 0. 4 0. 88 None 5 0. 4 0. 4 1. 64 Distinct 10 0. 8 0. 8 1. 63 Very distinct 10 0.8 0.8 l. 63 Very distinct 5 0. 2 0.3 0. 86 None 10 0. 4 0. 3 0. 88 None 15 0. 6 0. 3 0. 89 None 5 0. 4 0. 3 1.66 Moderate 10 0. 8 0. 3 1. 71 Very distinct l5 l. 2 0. 3 l. 72 Particularly distinct A yield of 9 4; percent was arrived at, for instance, as follows:

Example A solution containing by weight 11 parts of ammonium sulphate and 8.2 of sulphuric acid dissolved in 168 parts of water is admixed with such a quantity of nitric acid that the solution contains at least 1 part by weight HNO3 in 100 parts by volume of the solution (1. e. by weight 0.2 or by Volume 0.22 part of 1.40 sp. gr. nitric acid to 20 parts by volume of solution). In 20 parts by volume of this solution-heated to 95-97 C. 9.8 parts by volume of nitric acid of I 23.7 per cent by volume are allowed to run. Then, whileaconstantly stirring the liquid and maintaining the reaction temperature of 95 to 97 C. 10 parts by volume of an aqueous solution of 12.65parts by weight of ammonium thiocyanatev in 100 parts by volume are slowly introduced. This process is alternately repeated, carebeing taken to keep the volume of the reaction liquid as far as possible constant by means of an overflow arrangement; Acolumn connected to the reaction vessel serves to free-the gases, nitric oxides and hydrocyanic acid, generated by the reaction from the nitric acid which may be carried along with them. The hydrocyanic acid dissolved in the reaction liquid in accordance with its temperature is driven off by heating the reaction liquid to a higher temperature, which maybe done either after each partial operation directly in the reaction vessel'itself or in the overflow vessel connected thereto. The hydrocyanic acid is absorbed by an alkaline solu- .tion, and the remaining nitric oxides are converted into nitric acid in the well known manner.

What I claim is:

1. A method of producing hydrocyanic acid consisting in adding to a solution containing ammonium bi-sulphate, such quantity of free nitric acid that the concentration thereof always exceeds 1 per cent and then adding to said bath in alternate quantities, a solution of ammonium thiocyanate and nitric acid in equivalent proportions .for the oxidation reaction between ammonium thiocyanate and nitric acid.

2. A method of producing hydrocyanic acid consisting in dissolving 11 parts of ammonium sulphate and 8.2 parts of sulphuric acid in 168 parts of water, adding nitric acid to the solution of ammonium'sulphate and sulphuric acid in a quantity suchthat the said solution contains at least 1 part of .nitric acid in 100 parts of solution, heating 20 parts by volume of said solution to 9597 0., adding to said heated solution 9.8 parts by volume of nitric acid of 23.7 per cent strength, stirring said solution at a temperature 'tained substantially constant by removal of the surplus. I

.3. The method of producing hydrocyanic acid, consisting in adding to a solution of ammoniumbisulphate such an amount of nitric acid of desired concentration thatin the thus obtained mixture 1 per cent of free nitricacid. is present, and adding tosaid amounts of a' solution of nitric acid and of ammonium-thiocyanate that in the total amount of these additions such an amount of thenitric acid is used in excess that the concentration of the free nitric acid as regards its excess amounts to 1' per cent ofthe said acid present in the total amount of the reaction mixture.

' 4. The method of producing hydrocyanic acid, consisting in acting on a solution of ammonium thiocyanate with an excess of nitric acid in such manner that the concentration of nitric acid in the reaction mass is always in excess of lpercent. 5. The method ofproducing hydrocyanic acid consisting in alternately adding nitric acid and a solution of ammonium. thiocyanate in such a manner to a reaction mass. obtained by acting on a solution of ammonium thiccyanate with nitric acid that the concentration oinitric acid in the "total amountofthe reaction mixture is always in excess of 1 per cent.

KONRAD KELLER.

mixture such alternate 

